Conventionally, so-called wound cores have been known for improving yield of core materials used for producing laminated cores. The wound cores are produced by punching not ring-shaped core pieces, but a band of multiple segment core pieces from a magnetic steel strip, and winding and laminating the band of core pieces.
Specifically, as disclosed in, e.g., Japanese published unexamined publication No. 1-264548, Japanese published unexamined publication No. 8-196061, and Published Japanese translation of a PCT international application No. 2004-505595, arc-shaped segment core pieces are punched from a core material using molds, the segment core pieces having a prescribed number of slots and being connected with each other by connecting portions. Then, the connecting portions located in the outer peripheral area are bent, and the plural continuous core pieces are wound in a spiral form and laminated while inner circumferential portions of the adjacent core pieces are aligned.
However, in the conventional art disclosed in each of the publications, when the connecting portions are bent to position the multiple segment core pieces in an annular form, expanded parts are formed in the connecting portions in the thickness direction. The expanded parts create gaps between the laminated segment core pieces, thereby causing uneven thickness of manufactured laminated cores. In order to eliminate the gaps, for example, in the assembly of motors using the laminated cores, extra pressure treatments have been carried out on assembled laminated cores. However, it is difficult to remove the gaps completely even with the pressure treatments. Thus, the problems are that reduced efficiency and vibration in the motor using the laminated core are caused, thereby negatively affecting the quality of motors.
In view of the above circumstances, an object of the present invention is to provide a laminated core and a method for manufacturing the same, whereby high-efficient and high-quality products are manufactured without being affected by vertical expansion of the connecting portions.